Purified preparations of the DNA kinase from rat liver contain a phosphatase activity which removes the 3 feet-phosphate moiety from pTp and from the termini of deoxynucleotide chains. Several criteria indicate that both the DNA kinase and the 3 feet-phosphatase reactions are catalyzed by the same protein. If the phosphatase proves to be active at 3 feet-phosphate-terminated nicks, these reactions together with that of DNA ligase constitute a pathway for the repair of such nicks, and thereby support a role for DNA kinase in DNA repair.